The present invention relates to ink jet printing and, more particularly, to ink compositions used in ink jet printing.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant, which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc.
A requirement in wide format ink jet printers is the delivery of at least 500 ml of ink through a printhead before nozzles begin to fail to fire ink droplets. In order to achieve this, the ink composition is required to have desired physical characteristics including viscosity, surface tension and amount of dissolved gas. The optimized property levels are largely dependent on the printer design and printhead architecture.
During the ink delivery from an ink cartridge to a printer head, minute air bubbles present in the ink or within the ink cartridge gives flow resistance to the ink. In addition, when the ink head is repeatedly pressurized and depressurized during ink ejection, dissolved gases (e.g. dissolved oxygen and dissolved nitrogen) present in the ink tend to stagnate in the ink head causing the printhead to misfire during droplet ejection resulting in reduced printhead reliability. This is particularly true in piezoelectric print heads. Additionally, changes in both ink viscosity and surface tension can cause unreliable droplet ejection or droplet splashing which leads to reduced image quality. Typically, inks having a low surface tension (typically less than 40 mN/m) tend to have a faster drying time when compared to inks having a high surface tension (typically greater than 40 mN/m). However, inks having a high surface tension typically produce images of higher image quality as compared to the images produced by inks having lower surface tension.
Additionally, inks having properties allowing them to be more easily absorbed into a receiver also exhibit shorter drying times. These ink properties can be described in terms of advancing (forward, etc.) contact angle. For example, inks having advancing contact angles greater than 60xc2x0 relative to a porous receiver, typically, do not penetrate the pore system of the receiver, and, as such, are not absorbed by the receiver. This can result in longer drying times and can cause an increased likelihood of image smearing because the ink resides on the receiver surface for an extended period of time.
U.S. Pat. No. 5,683,500, which issued to Kawasumi et al. on Nov. 4, 1997, optimizes an ink composition used in a writing instrument so as to reduced writing defects including uneven ink density and skips in a drawn line. U.S. Pat. No. 5,833,744, which issued to Breton et al. on Nov. 10, 1998, optimizes an ink composition by adding a paper specific surfactant having a paper pulp debonding agent. U.S. Pat. No. 6,288,156 B1, which issued to Higashiyama et al. on May 8, 2001, optimizes an ink composition for use over a range of temperatures.
An object of the present invention is to optimize the above described physical properties of an ink composition so that desired quantities of ink can be delivered by a printhead to a receiver reliability and consistently over time.
According to a feature of the present invention, an ink cartridge includes a housing having a front side wall, a back side wall opposite the front side wall, a pair of opposed left and right side walls separating the front and the back side walls, and a bottom wall, the walls defining an internal cavity within the housing. An ink container is located within the internal cavity and filled with a liquid ink. The liquid ink has a dissolved gas content of less than 3 ppm as measured on the basis of the amount of dissolved oxygen gas at 20xc2x0 C., a static surface tension at 25xc2x0 C. of greater than 34 dynes/cm, and an advancing contact angle relative to an ink receiving receiver of less than about 55xc2x0 at room temperature.
According to another feature of the present invention, an ink composition includes a colorant and an aqueous carrier. The ink composition has a dissolved gas content of less than 3 ppm as measured on the basis of the amount of dissolved oxygen gas at 20xc2x0 C. at 20xc2x0 C., a static surface tension at 25xc2x0 C. of greater than 34 dynes/cm, and an advancing contact angle relative to an ink receiving receiver of less than about 55xc2x0 at room temperature.
According to another feature of the present invention, a method of filling an ink cartridge includes providing a housing having a front side wall, a back side wall opposite the front side wall, a pair of opposed left and right side walls separating the front and the back side walls, and a bottom wall, the walls defining an internal cavity within the housing; providing an ink container; positioning the ink container within the internal cavity; and filling the ink container with a liquid ink having a dissolved gas content of less than 3 ppm as measured on the basis of the amount of dissolved oxygen gas at 20xc2x0 C., a static surface tension at 25xc2x0 C. of greater than 34 dynes/cm, and an advancing contact angle relative to an ink receiving receiver of less than about 55xc2x0 at room temperature.
According to another feature of the present invention, an ink cartridge includes an ink container filled with a liquid ink. The liquid ink has a dissolved gas content of less than 3 ppm as measured on the basis of the amount of dissolved oxygen gas at 20xc2x0 C., a static surface tension at 25xc2x0 C. of greater than 34 dynes/cm, and an advancing contact angle relative to an ink receiving receiver of less than about 55xc2x0 at room temperature.